1. Field of the Invention
The present invention relates to an interlock stitch sewing machine for blindstitch hemming with a slippage preventing device. More particularly, the invention relates to an interlock stitch sewing machine for blindstitch hemming with a slippage preventing device which is constructed so as to prevent such slippage that is liable to occur in the blindstitch hemming of a tubular article such as T-shirts or underwear. Specifically, of fabric portions stacked by a top-stitching at the fabric end, a lower fabric portion slips, or a locally deformed portion due to a cutting error is present at the edge of the lower fabric portion.
2. Description of the Prior Art
FIG. 11 illustrates a construction of a major part of a three-needle interlock stitch sewing machine for blindstitch hemming which has conventionally being in general use. In this sewing machine, paired front and rear feed dogs (which are not shown because this is known) which feed a tubular article W in a sewing direction indicated by the arrow Y, are disposed underneath a throat plate 2 provided on the upper surface of a sewing machine bed 1. A pressure foot 3 that presses the article W against the upper surface of the throat plate 2, and three needles 4 that are movable vertically reciprocally are supported on an arm 5 disposed above the throat plate 2. In front of the pressure foot 3 and a needle location 6 formed in the throat plate 2, a top-stitching width guide 7 and a fabric edge guide 8 are oppositely disposed in a direction orthogonal to the sewing direction Y. The top-stitching width guide 7 defines a top-stitching width h toward the back of the edge of the article W, and makes contact with a bent portion W2a formed by a lower fabric portion W1 and an upper fabric portion W2 overlying thereon, to guidedly feed the bent portion W2a in the sewing direction Y. The fabric edge guide 8 makes contact with an edge W1a of the lower fabric portion W1 to guidedly feed the edge W1a in the sewing direction Y.
In the three-needle interlock stitch sewing machine for blindstitch hemming so constructed, the rotation of the sewing machine is started when the operator sets the article W on the surfaces of the bed 1 and throat plate 2, while the end of the article W is folded downwardly through the top-stitching width guide 7, so as to obtain an approximately constant top-stitching width h. As the sewing machine is rotated, the fabric portions W2 and W1 which are stacked at the top-stitching are subsequently fed in the sewing direction Y along the upper surface of the throat plate 2, by up and down movements of the paired feed dogs and by the pressure foot 3 cooperating with the movements of the feed dogs. Then, when the fabric portions W2 and W1 reach the needle location 6, the three needles 4 and a looper (not shown) cooperate to form a stitch Wa that is wide in the direction in which the fabric portions W2 and W1 cross at a right angle to the sewing direction Y, as shown in FIG. 12, thereby performing a predetermined interlock stitch sewing.
In such a blindstitch hemming sewing, as indicated by virtual line in FIG. 11, the bent portion W2a of the upper fabric portion W2 and the edge W1a of the lower fabric portion W1 make contact with the top-stitching width guide 7 and fabric edge guide 8, respectively, thereby to be guidedly fed in the sewing direction Y. That is, the conventional interlock stitch sewing machine for blindstitch hemming is so constructed that a blindstitch hemming while retaining a constant top-stitching width h of the lower fabric portion W1, is carried out only by slidingly guiding the ends of the upper and lower fabric portions (i.e., the bent portion W2a and the edge W1a), by the top-stitching width guide 7 and fabric edge guide 8 oppositely disposed in front of the needle location 6.
In the above sewing machine, however, of the fabric portions W2 and W1 stacked at the top-stitching, the lower fabric portion W1 is extremely hard to see by the operator's eye. It is therefore difficult that the top-stitching toward the back of the fabric end is always kept constant only by the top-stitching width guide 7 and fabric edge guide 8. It is also very difficult to adjust the top-stitching width in the course of the fabric feed. Thus, the stacked fabric portions tend to be guidedly fed to the needle location 6 in the state that the edge W1a of the lower fabric portion W1 has a position error, thereby causing slippage. In addition, even if a locally deformed portion is present at the edge W1a of the lower fabric portion W1, it is difficult to observe the deformed portion by the eye during the sewing operation. Therefore, when the deformed portion is large in the sewing direction, a faulty sewing such as slippage is liable to occur. Hence, it has conventionally been indispensable to conduct, after sewing operation, a product inspection to visually inspect for faulty sewing such as slippage.